An organic light emission phenomenon is an example of converting current into visible rays by an internal process of a specific organic molecule. A principle of the organic light emission phenomenon is as follows.
When an organic material layer is positioned between an anode and a cathode, if a voltage is applied between two electrodes, electrons and holes are respectively injected from the cathode and the anode into the organic material layer. The electrons and the holes which are injected into the organic material layer are recombined to form excitons, and light is emitted while the excitons fall down to a bottom state again. In general, an organic light emitting diode using this principle may be constituted by a cathode, an anode, and an organic material layer positioned therebetween, for example, an organic material layer including a hole injection layer, a hole transport layer, a light emitting layer, and an electron transport layer.
A material used for the organic light emitting diode is mostly a pure organic material or a complex compound where an organic material and metal form a complex, and may be classified into a hole injection material, a hole transport material, a light emitting material, an electron transport material, an electron injection material, and the like according to the purpose thereof. Herein, an organic material having a p-type property, that is, an organic material that is easily oxidized and has an electrochemically stable state during oxidation, is mostly used as the hole injection material or the hole transport material. Meanwhile, an organic material having an n-type property, that is, an organic material that is easily reduced and has an electrochemically stable state during reduction, is mostly used as the electron injection material or the electron transport material. As a light emitting layer material, a material having both p-type and n-type properties, that is, a material having a stable form in both oxidation and reduction states is preferable. Also, a material having high light emitting efficiency for converting the exciton into light when the exciton is formed is preferable.
In the art, there is a demand for developing an organic light emitting diode having high efficiency.